The present invention relates to a process for constructing a chemical plant for the production of cyclohexanone.
Cyclohexanone is an intermediate in the production of, amongst other compounds, adipic acid and caprolactam. These are monomers commonly used in the production of polyamide-6,6 and polyamide-6, respectively. The majority of cyclohexanone for use in producing caprolactam is produced by oxidation of cyclohexane, using atmospheric oxygen. Typically, cyclohexane is produced from hydrogenation of benzene. Oxidation of cyclohexane yields a mixture of cyclohexanol and cyclohexanone and the precursor hydroxyl hydroperoxide which is then thermally and/or catalytically decomposed to produce additional cyclohexanol and cyclohexanone, and a variety of by-products. Cyclohexane constitutes the vast majority of the resulting mixture from the oxidation unit because the conversion rate of the reaction is low. Cyclohexane is removed by distillation and recycled in the process. Cyclohexanone is then separated by distillation from the mixture comprising cyclohexanol, cyclohexanone, unreacted cyclohexane and by-products. Cyclohexanol may also be recovered by distillation and optionally converted to cyclohexanone by dehydrogenation.
One alternative process for the production of cyclohexanone is by the catalytic reduction of phenol with hydrogen, for example using a palladium-comprising catalyst. The reduction of phenol with hydrogen can be performed in the gas phase or in the liquid phase, described in, for example, Michael Tuttle Musser; Cyclohexanol and Cyclohexanone in Ullmann's Encyclopedia of Industrial Chemistry Published Online: 15 Oct. 2011 DOI: 10.1002/14356007.a08_217.pub2 Copyright © 2002 by Wiley-VCH Verlag GmbH & Co. KGaA (Musser); and J. F. Van Peppen, W. B. Fisher and C. H. Chan; ‘Phenol Hydrogenation Process’ in Chemical Industries, 22 (‘Catalysis of Organic Reactions’; Ed. R. L. Augustine); Marcel and Dekker, N.Y., 355-372; (1985)). A mixture comprising cyclohexanol, cyclohexanone, unreacted phenol and by-products is produced. Separation of cyclohexanone from this mixture may be made by distillation. The composition of such a mixture is vastly different to that produced by the oxidation of cyclohexane. Accordingly, the apparatus required for the hydrogenation of phenol is different to that required for the oxidation of cyclohexanone.
Chemical plants for the production of cyclohexanone and cyclohexanol by oxidation of cyclohexane are known in the art, also described in, for example, Musser. Chemical plants have a maximum capacity. A plant may in practice be operated at capacities below this. However, there arises a problem when it is desired to increase the capacity of a chemical plant above the maximum of the current design, for example when increased demand of product is experienced.
One option for expansion is to build a new plant. For example, an existing plant could be substantially copied to provide the increased capacity. A major drawback of this approach is the high cost. Alternatively, the existing plant could be modified by increasing capacity of the rate-limiting components of the plant, a form of “de-bottlenecking”. This could be for example by replacing an existing component with another component having a larger capacity, or adding a duplicate component. However, where such rate-limiting components are complex, it may be prohibitively costly to replace or expand them.